help with 293T

Hi, i just join to this page.
Actually i had 6 dishes of 293T which i transformed them and i keep in 37C with 5% CO2 but suddenly TM of incubator increase and get into 40C. my cells was in this TM for 1 hours.
the cells suppose to express EGFP. after transfection i check them, they are ok except one of them which don't show any expression.
i am thinking it can be happen because they are in high TM for hour?